The field of the present invention is that of an arrangement of a direct injection stratified charged (DISC) gasoline engine and methods of operation thereof. More particularly, the field of the present invention is that of a DISC gasoline engine which has a boost device to extend the range of stratified charging of the engine.
In a carbureted four cycle engine, gasoline is added to the incoming air in a carburetor. The gas and air mixture is then admitted into a cylinder combustion chamber by an inlet poppet valve during an intake stroke of a reciprocating piston, which is slidably mounted within the combustion chamber. In a modern port fuel injected (PFI) engine, fuel injectors input a specific measured amount of fuel at ports adjacent the inlet poppet valves. In a manner as previously described, the fuel and air are admitted into the combustion chambers.
Recent advancements in fuel system technology have allowed implementation of a direct fuel injected gasoline engine. In a direct fuel injected engine, air is also admitted into the combustion chamber by a poppet valve. However, each combustion chamber has a separate fuel injector which charges fuel directly into the combustion chamber.
A direct injection engine can operate in a manner similar to a conventional PFI engine by injecting fuel during an inlet stroke of the piston. Normally when the fuel is injected during the inlet stroke of the piston, there is time before ignition for substantial mixing of the fuel with the air. Accordingly, the air to fuel ratio (AFR) of the mixture within the combustion chamber will be essentially homogenous. Engines can operate with homogeneous charge at AFRs ranging from slightly rich of stoichiometry to approximately 24:1. The rich and lean AFR limits depend on specific engine design.
With appropriate design, a direct injection engine can also operate in an unthrottled manner similar to that of a diesel engine. This type of engine is called a direct injection stratified charge (DISC) engine. In the DISC engine the injection of fuel into the combustion chamber may be delayed until the compression stroke of the piston. With this strategy, the fuel does not have as much time to mix with the air. Accordingly, the AFR within the combustion chamber is stratified. Typically, the highest concentration of fuel will be in an area adjacent to the spark plug, which will have a stoichiometric mixture or a mixture slightly rich of stoichiometry. The other regions of the combustion chamber will be very lean. The resultant overall AFR may range from 20:1 to 50:1. The rich and lean AFR limits depend on specific engine design. Typically the preferable AFR will be 25:1 to 40:1.
The DISC engine has a major advantage in fuel economy by virtue of its high AFR with stratified charge operation. The increased air requirements, compared to conventional engines operating at stoichiometry, lead to improved fuel economy through reduction in pumping work and higher thermal efficiency. This decrease in fuel consumption results in lower CO2 emissions. This line of reasoning also holds for a homogeneous charge that is lean of stoichiometry regardless of the engine type.
Due to high air flow requirements, stratified and homogeneous lean operation is restricted to low speed and torque conditions for naturally aspirated DISC engines. At higher torque or speed levels, prior DISC engines could not maintain the mandated high AFR. Since operating at stoichiometry or rich of stoichiometry is less fuel efficient, fuel economy suffers at higher torque and speed conditions.
It would be desirable to provide a DISC gasoline engine arrangement which could extend the stratified charge and/or homogeneous lean charge operation to a wider engine operational range.
The present invention brings forth a boosted, four cycle, spark ignited, direct injection, internal combustion engine arrangement that is capable of operating with a stratified charge. The engine arrangement of this invention improves fuel economy and CO2 emissions. The above-noted improvements are accomplished by pressurizing the manifold feeding the combustion chambers such that the DISC engine of the present invention maintains a stratified charge operation in a higher range of engine speed and torque levels. Additionally, a preferred embodiment of the present invention provides for improvements in vehicle emissions. In the alternate preferred embodiment the DISC engine of the present invention is boosted using a variable geometry turbocharger (VGT). The VGT allows direct control of exhaust manifold conditions leading to enhanced control of EGR and exhaust gas temperatures, which can improve tailpipe emissions. The use of the VGT allows the preferred engine arrangement of the present invention to go from a stratified charge operation to lean homogeneous charge operation at high levels of torque and/or speed demand. The VGT also allows the engine arrangement of the present invention to remain in the lean homogeneous charge operation for a higher percentage of peak engine output. At wide-open throttle (WOT) the preferred engine arrangement can revert to a stoichiometric or rich homogeneous operation. To allow engine operation at homogeneous charge and to enhance the control of the AFR during stratified operation, there is provided a throttle body. To further enhance the operation of the engine arrangement there is optionally provided an intercooler.
These and other features and advantages of this invention will become apparent to those skilled in the art from the following detailed description and accompanying drawings illustrating features of this invention by way of example.